In conjunction with a demand for electronic instruments having a smaller size, there has been an increasing demand for batteries having a smaller size to be used for their power source. In order to satisfy such a demand for batteries, thinned batteries have been taken into consideration. Known as such batteries are those in which an electrode and an electrolytic solution or the like are sealed into a bag made of a plastic or a combination of a plastic and a metal which are bonded together. Since the reliability of such batteries depends on its hermetic property, various studies have been made as explained in the following.
For example, Japanese Patent Application Laid-Open No. 56-71278 discloses a sheet-like battery. In this battery, while the part occupied by the heat-fusing portion is reduced, a lead which has been coated with a resin beforehand is used to improve the reliability of its heat fusion with respect to the bag.
The bag for sealing the battery system disclosed in Japanese Patent Application Laid-Open No. 56-71278, however, is formed by a single iodine-resistant fluorine resin. Consequently, in the case of a nonaqueous electrolyte battery whose electrolytic solution is volatile or of an organic solvent system, there is a strong tendency for the electrolytic solution to penetrate through the bag to leak out or for moisture to infiltrate therein from the outside, thereby yielding an inferior hermetic property.
On the other hand, Japanese Patent Application Laid-Open No. 3-62447 discloses a battery in which, as a material for a seal portion of a sealing bag, acrylic acid modified polyethylene or acrylic acid modified polypropylene is used.
The battery disclosed in Japanese Patent Application Laid-Open No. 3-62447, however, is disadvantageous in that, since a highly hygroscopic acrylic acid modified polyolefin is used in the bag, moisture is likely to infiltrate therein.
Accordingly, it is an object of the present invention to provide a nonaqueous electrolyte battery having high blocking properties against the nonaqueous electrolytic solution and steam.